The typical human heart 100, a portion of which is shown in FIG. 1, includes a right ventricle, a right atrium 102, a left ventricle, and a left atrium 104. The right atrium 102 is in fluid communication with the superior vena cava 106 and the inferior vena cava 108. A tricuspid valve separates the right atrium 102 from the right ventricle. On the interatrial septum 110, which is the wall separating the right atrium 102 from the left atrium 104, is the fossa ovalis 112, a thin-walled, recessed area. In the heart of a fetus, the fossa ovalis 112 is open (patent foramen), permitting fetal blood to flow between the right and left atria 102 and 104, bypassing the fetal lungs in favor of the placental blood flow. In most individuals, this opening closes after birth.
A wide variety of diagnostic and therapeutic procedures have been developed in which a catheter is transluminally advanced into various chambers and across valves of the heart. The most difficult chamber of the heart to access with a catheter is the left atrium 104. Access to the left atrium 104 through the pulmonary artery is not possible. Approaches from the left ventricle are difficult, may cause arrhythmias, and may present difficulty in obtaining stable catheter positioning. Accordingly, the presently preferred method of accessing the left atrium 104 is through a transseptal approach, achieved by catheterization of the right atrium 102 with subsequent penetration of the interatrial septum 110. The reduced wall thickness and location of the fossa ovalis 112 make it a useful access point for a transseptal access puncture. The current methods of puncturing involve accessing the septum from the inferior vena cava 108. There is no device currently available that allows safe puncture from the superior vena cava 106.
A variety of risks are attendant to transseptal catheterization, in addition to the risks associated with normal heart catheterization. The primary additional risk is associated with inaccurate identification and localization of the interatrial septum 110 and the fossa ovalis 112 in particular. Improper placement of the catheter tip prior to the transseptal puncture presents the risk of puncture of tissue other than the interatrial septum 110, such as the aorta and/or the posterior wall of the right or left atrium 102 or 104. For this reason, catheterization is often accompanied by fluoroscopy or other visualizing techniques to assist in properly locating the catheter tip in relation to the septum 110.
The objectives of left atrial access can be either diagnostic or therapeutic. One diagnostic use is pressure measurement in the left atrium 104. In the setting of an obstructed mitral valve (mitral stenosis), left atrial access allows a determination of the pressure difference between the left atrium 104 and left ventricle. Left atrial access also allows entry into the left ventricle through the mitral valve. This is desirable when a mechanical aortic valve is in place. The advent of aortic valve replacement with mechanical artificial valves, and the increase in the aged population and growing longevity of that population subsequent to aortic valve replacement, brings a greater need to evaluate the late stage functionality of such artificial valves.
Diagnostic measurement of the left ventricular pressures is, therefore, desirable to allow evaluation of mechanical artificial aortic valves post-replacement. Crossing these mechanical artificial valves retrograde from the aorta may be nonoptimal; therefore, access to the left ventricle by an antegrade route using a transseptal puncture is generally the preferred approach. Once a catheter has been placed in the left atrium 104 using the transseptal approach, access to the left ventricle can be gained by advancing catheters across the mitral valve.
Many diagnostic indications exist for left atrial pressure measurements in addition to evaluating the functionality of artificial mitral valves. Other diagnostic indications for accessing the left ventricle via the antegrade transseptal approach include aortic steno sis, when a cardiologist is unable to pass a catheter retrograde into the left ventricle, and some disease states where the antegrade approach is considered preferable, such as subaortic obstruction.
Presently, the therapeutic objectives of left atrial access are primarily two-fold. The first is mitral valvuloplasty which represents an alternative to surgical procedures to relieve obstruction of the mitral valve. The second main therapeutic objective is for electrophysiological intervention in the left atrium 104 via catheter ablation. Catheter ablation involves the placement of energy, typically radio frequency (RF) from an electrode, through a catheter into various areas of the heart 100 to eradicate inappropriate electrical pathways affecting the heart function. When these locations are in the left atrium 104, the catheter through which the RF electrode is placed typically is itself placed into the left atrium 104 with transseptal catheterization. More recently, therapeutic treatment of the left atrial appendage to reduce the risk of embolic stroke has also been proposed.
In addition to the above, left atrium 104 access may be desirable for pulmonary vein isolation, atrial appendage closure, patent foramen ovalis closure, and aortic valve replacement or valvuloplasty. Despite clinical acceptance of a wide variety of procedures which require access to the left atrium 104, however, significant room for improvement remains in the actual access technique. For example, the step of locating an appropriate site on the interatrial septum 110, such as the fossa ovalis 112, is highly technique-dependent and can be inaccurate. Such inaccuracy may increase procedure time and/or create a risk that the needle will pierce a heart structure in an unnecessary and potentially undesirable location. Another problem is that the needle may slip while advancing toward the interatrial septum 110, resulting in an inadvertent puncture into surrounding structures within/defining the right atrium 102 before the needle even reaches the interatrial septum 110. This type of undesired puncture is particularly a risk when the left atrium 104 is large and causes the interatrial septum 110 to bulge into the right atrium 102.
In addition to the example of accessing the left atrium 104 through the interatrial septum 110, there are other occasions when it may be desirable to access a body cavity from a nearby hollow structure (vascular or otherwise) which is easier to access. Broadly, “inside-out” access to a number of different body structures could be useful in many different surgical situations. For example, a surgeon may wish to provide a cannula in the heart 100, place a conduit in an artery or vein, or to connect two adjacent body cavities by puncturing from one to the other and placing a conduit between the cavities.
Moreover, and more broadly, there are many reasons for a surgeon to desire precise location of a target site within the body, whether or not the target site is to be punctured.